1. Field of the Invention
The present invention relates to a supporting chuck for adsorbing and supporting a flat plate shaped object such as a semiconductor wafer. More particularly, the present invention relates to a wafer space supporting apparatus installed on the supporting chuck and a method for fabricating the same.
2. Description of Background Art
Currently, for semiconductor products to be competitive, they must be of high quality but low price. High integration is essentially required to achieve low-cost semiconductor products. Highly integrated semiconductor devices require a scale-down process including steps of making gate oxide layers of transistors thinner and their channels shorter. Accordingly, many different semiconductor fabricating processes and related processing systems have been recently developed to create highly integrated semiconductor devices.
In a deposition step of a semiconductor fabricating processes, a gas or other type of material is applied directly or indirectly to a semiconductor wafer or any other object to be produced. The layer quality resulting from the deposition process is mainly determined by parameters such as atmospheric conditions including temperature and pressure of a processing chamber, catalyst gas and reactant gas. It is well known that these same parameters determine the layer quality resulting from an etching process.
In the deposition processing system or etching processing system, the substrate to be fabricated, such as a wafer, must be statically supported inside a reaction chamber in order to obtain a uniform layer. Therefore, a substrate supporting chuck has been widely used for supporting the substrate in semiconductor processing systems. At high temperatures, such as in a high temperature physical vapor deposition (PVD) apparatus, a ceramic electrostatic chuck is used for retaining an object to be fabricated, i.e. a semiconductor wafer, at a fixed position during a period of processing. Such an electrostatic chuck includes more than one electrode embedded in its body. The chuck is made out of various kinds of ceramic materials. These materials may be typical aluminum nitride, a special type of alumina doped with a metal oxide such as titanium oxide, or other ceramic materials having similar electric resistances, but which differ in their other characteristics. These types of ceramic materials have partial conductivity at high temperatures.
When a chucking voltage is applied to the electrodes, the conductivity of the ceramic material at high temperatures enables a wafer to become adsorbed and stuck to the upper surface of the support chuck by the Johnsen-Rahbek effect. A chuck of this kind has been disclosed in U.S. Pat. No. 5,111,121 to Gries et al.
An inconvenience of using the ceramic electrostatic chuck is that particles, a source of contamination, are generated in the fabricating process. When the electrostatic adsorption generates friction at the lower surface of a wafer, that is, between the back side of the wafer and a surface of the ceramic chuck, particles are produced causing a hard defect.
U.S. Pat. No. 5,825,607 issued Oct. 20, 1998 to Burkhart discloses a method for reducing the amount of contamination particles being adsorbed onto the back side of a wafer.
With reference to FIGS. 1 and 2, a wafer 116 is propped apart from a surface 102 of ceramic electrostatic chuck 104 by a wafer spacing mask 100 which is constructed with insulating regions 113 at a surface 102 of the ceramic electrostatic chuck 104 and spacing masks 112 deposited on the insulating regions 113. Therefore, it becomes difficult for particles to become adsorbed onto the back side of the wafer 116.
In other words, the prior art described above has an advantage in reducing both the amount of contamination particles that are adsorbed onto the back side of the wafer and the leakage current flowing through the wafer supported by the electrostatic chuck. The prior art described above has a disadvantage, however, in that the wafer is supported such that it is fixed, but the wafer expands and contracts according to its temperature, thereby causing friction between the upper part of the spacing mask 112 and the back side of the wafer. Hence, in the aforementioned patent, the friction causes another type of hard defect.
Now, generation of the hard defect will become more apparent in the following detailed description. A wafer to be used for fabricating a number of semiconductor devices at one time goes through thermal stress in the course of deposition and etching processes. The thermal stress appears when the wafer repeatedly expands and contracts while moving from a high temperature process to a low temperature process or vice versa. At this time, a thermal expansion coefficient of the wafer and that of the spacing mask installed on the electrostatic chuck are different. Thus, friction is generated between the back side of the wafer and the upper surface of the electrostatic chuck or the upper part of the supporting spacing mask by repetition of expansion and contraction processes. Such a phenomenon becomes worse in a multi-chamber system in which an in-situ process is consecutively performed with various changes in temperature.
As a result, the friction generated between the chuck holding the wafer and the back side of the wafer by expansion and contraction may cause scratches on the back side of the wafer and particles on the back side of the substrate of the electrostatic chuck. Thus, there may be problems of increasing hard defects in the fabricating processes and reducing the lifetime of the electrostatic chuck. In addition, the deformation of the wafer caused by the thermal stress may cause significant deterioration to the functionality and reliability of a micro semiconductor device.
In other words, there is a problem with the conventional electrostatic chuck for supporting an object to be fabricated in that because the object supporting part is fixed, there is no compensation for thermal expansion and contraction of the object, thereby resulting in friction between the object and the supporting device, and deteriorating the reliability of the processing system.
It is a feature of an embodiment of the present invention to solve the aforementioned problems and provide a method for minimizing friction generated by thermal expansion and contraction of an object to be fabricated.
It is another feature of an embodiment of the present invention to provide an apparatus that minimizes hard defects incurred during a process in which a supporting chuck fixes an object such as a wafer to be fabricated.
It is another feature of an embodiment of the present invention to provide a wafer space supporting apparatus and a method for fabricating the same that relieves the maximum level of stress caused by thermal expansion or contraction of an object to be fabricated and adjusts itself to supporting the object to compensate for thermal expansion and contraction.
It is still another feature of an embodiment of the present invention to provide an apparatus that can effectively restrict generation of particles that become attached to the back side of a wafer, and a method for fabricating the same.
It is still another feature of an embodiment of the present invention to provide an apparatus that can effectively restrict physical stress applied to the wafer while the wafer is held.
In order to accomplish the aforementioned features in accordance with an embodiment of the present invention, an apparatus is provided for supporting an object to be fabricated, wherein the object is supported spaciously apart from a supporting surface of a chuck comprising:
a plurality of sliding pockets sunken into the supporting surface of the chuck; and
a plurality of sliding pads respectively floating-coupled in the sliding pockets such that the sliding pads are spaced apart from the supporting surface in order to provide adaptive support to the object to be fabricated to compensate for the object""s expansion and contraction.
Preferably, each sliding pocket includes a magnetic pocket body having an internal space that confines a part of the sliding pad to prevent its escape and a magnetic base cover spaced apart from a lower part of the sliding pad for enabling the sliding pad to be connected to or disconnected from the pocket body in one direction.
At this time, the sliding pad may include a sliding body with parts having a magnetic polarity identical to a magnetic polarity of corresponding parts of the pocket body and base cover to allow the sliding pad to move freely in the internal space of the pocket body with no contact, and a supporting member installed at a part of an upper surface of the sliding body.
In accordance with another feature of an embodiment of the present invention, a method for fabricating the wafer space supporting apparatus comprises:
sinking a plurality of sliding pockets into a supporting surface of a chuck; and
forming a plurality of sliding pads respectively floating-coupled in the sliding pockets for supporting an object to be fabricated such that the sliding pads are spaced apart from the supporting surface so that the object to be fabricated may be supported adaptively to compensate for its expansion and contraction.
Advantages of the apparatus of the present invention as described above include prevention of particles being stuck to a back side of the object to be fabricated, such as a wafer, and minimization of physical stress to the object to be fabricated that may cause deformation of the object by the ability of the apparatus to support the object tightly, but adaptively to compensate for expansion and contraction of the object, such as a wafer.
These and other features of the present invention will be readily apparent to those of ordinary skill in the art upon review of the detailed description that follows.